(a) Technical Field
The present disclosure relates to a method for reducing the vibration caused by gear backlash in a drive system for a hybrid vehicle. More particularly, the present invention relates to a method for reducing the vibration that is caused by gear backlash in a drive system for a hybrid vehicle. Preferably, the present invention features methods that can reduce backlash vibration that is caused by gear elements between a motor and driving wheels when the hybrid vehicle is suitably driven by the motor.
(b) Background Art
Various types of hybrid vehicles such as fuel cell hybrid vehicles, plug-in hybrid vehicles, hybrid electric vehicles, etc. have an electric vehicle (EV) mode, in which the vehicle is driven only by an electric motor that suitably converts electrical energy from a high voltage battery into mechanical energy, and a regenerative braking (RB) mode, in which the mechanical energy of an engine and driving wheels is suitably recovered (or regenerated) by the electric motor, suitably converted into electrical energy by an inverter, and suitably stored in an energy storage device such as a battery.
Preferably, these hybrid vehicles include various gear elements having, for example, backlash characteristics such as a transmission, a final reduction gear, etc. between the electric motor and the driving wheels. However, the hybrid vehicles are not sufficiently equipped with damping elements such as a torsional damper that suitably absorbs the backlash of these gear elements, and thus vibration is generated when the direction of effective torque is changed by the gear elements.
Accordingly, vibration is generated mainly during creep running due to accumulation of backlash of the gear elements between the motor and the driving wheels, which as a result has an effect on the driving performance of the vehicle, and may be contrary to the users' expectation of environmentally-friendly vehicles.
A backlash mechanism, which is a phenomenon in which, for example, the backlash of the gear elements between the motor and the driving wheels occurs during the EV mode in which the vehicle is preferably driven only by the motor, will be described with reference to FIG. 1 below.
FIG. 1 is a schematic diagram showing gears suitably modeled as a spring system.
It takes a certain amount of time for the motor torque to be suitably transmitted to a drive shaft. Accordingly, the required time may be explained as the time required for the gears such as an automatic transmission to be suitably aligned in the driving direction, i.e., as a delay time due to the gear backlash and a gap between the respective gears.
As shown in FIG. 1, a dead zone of the motor torque is suitably created by a gap 30 preferably formed by a gear tooth between a first gear 10 and a second gear.
The motor torque preferably passing through the dead zone by the gear tooth is shown as a dashed-dotted line in FIG. 2, from which it can be seen that the motor torque transmission is suitably interrupted by the gear backlash unlike the linear torque (shown as a dotted line in FIG. 2) that is normally transmitted.
The vibration generated when the direction of the effective torque is suitably changed by the gear elements is described with reference to FIG. 1 below.
As shown in FIG. 1, where the gears are modeled as an exemplary spring system, vibration is suitably generated in the spring system at a point of time when the direction of the effective torque between the first and second gears is preferably changed.
That is, the torque is preferably transmitted to the second gear 20 when the first gear 10 suitably operates in the arrow direction. However, as shown in the spring system of FIG. 1, vibration is suitably generated in the spring system during the torque transmission due to “compression release of a front spring 40”, “a physical gap 30 between first and second gears”, and “compression of a rear spring 50”. As a result, vibration is suitably generated when the direction of the effective torque is changed by the gear elements.
Accordingly, when the torque is suitably transmitted from the first gear 10 to the second gear 20, the region in which “the compression release of the front spring 40”, “the physical gap 30 between first the and second gears”, and “the compression of the rear spring 50” are made preferably corresponds to a null torque zone.
Preferably, the torque range is in the null torque zone where, preferably, “the compression release of the front spring 40”, “the physical gap 30 between first the and second gears”, and “the compression of the rear spring 50” are suitably made is considerably less than a significant torque level (e.g., 5 Nm with respect to a transmission input shaft).
As a result, the motor torque transmission is interrupted by the gear backlash and thus vibration is generated, which effects the driving performance of the vehicle.
Conventionally, various methods have been proposed to address the vibration that is generated, such as, but not limited to, a passive damping method that suitably applies a physical damping element such as a torsional damper, an active damping method of a closed loop type that suitably exerts a damping force in the reverse direction of vibration, and a torque profile control method that suitably suppresses the occurrence of vibration by changing the input torque of the backlash mechanism. In the case of the passive damping method, it is difficult to solve a packaging problem for the drive system including the gear elements. In the case of the active damping method, it is necessary to separately configure a high-performance sensor and an observer. Also, in the case of the torque profile control method, it may reduce the vibration due to a reduction in torque change rate to some degree; however, the response deteriorates, and the vibration may increase due to a model error when the reverse phase torque based on the vibration model is added.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.